The present invention relates to the fabrication of three-dimensional (3D) objects using extrusion-based layered manufacturing systems. In particular, the present invention relates to an extrusion head that extrudes multiple materials for building 3D objects with a single drive motor.
An extrusion-based layered manufacturing system (e.g., fused deposition modeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) is typically used to build a 3D object from a CAD model in a layer-by-layer fashion by extruding a flowable build material, such as a thermoplastic material. The build material is extruded through a nozzle carried by an extrusion head, and is deposited as a sequence of roads on a base in an x-y plane. The extruded build material fuses to previously deposited build material, and solidifies upon a drop in temperature. The position of the extrusion head relative to the base is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D object resembling the CAD model.
Movement of the extrusion head with respect to the base is performed under computer control, in accordance with build data from a host computer. The build data is obtained by initially slicing the CAD model of the 3D object into multiple horizontally sliced layers. Then, for each sliced layer, the host computer generates a build path for depositing roads of build material to form the 3D object.
In fabricating 3D objects by depositing layers of build material, supporting layers or structures are built underneath overhanging portions or in cavities of objects under construction, which are not supported by the build material itself. A support structure may be built utilizing the same deposition techniques by which the build material is deposited. The host computer generates additional geometry acting as a support structure for the overhanging or free-space segments of the 3D object being formed. Support material is then deposited pursuant to the generated geometry during the build process. The support material adheres to the build material during fabrication, and is removable from the completed 3D object when the build process is complete.